30 degrees and x are complementary angles, which means that they're adjacent angles that add up to 90 degrees. How you know they add up 90 degrees is because of the supplementary angles, which are angles that have a sum of 180 degrees. x + 30 + 90 = 180, using algebraic steps you get x = 60. There are other ways of getting to x = 60, but that's the quickest.
x = 60
